1. Field of the Invention
The present invention relates to a frame for an inflatable catamaran. An inflatable catamaran comprises two spaced inflatable tubes which form the hulls of the boat, the tubes being secured together by a rigid support which generally is in the form of a frame. The frame generally provides one or more seats and possibly also strong-points to which masts or oars or an engine can be secured.
2. Description of the Prior Art
A variety of different catamarans or catamaran type frames have been proposed; for example, U.S. Pat. No. 4,284,024 (Montgomery) discloses a simple form of frame in which a rigid longitudinal beam is secured along the top of each hull and a pair of spaced cross beams are secured between the longitudinal beams, to form a frame. This frame is secured together simply by fastening the components together, so that the frame must be virtually completely dismantled to transport or store the catamaran. A further drawback of this design is that the longitudinal beams are the same length as the hulls, and therefore are over-long for convenient storage or transport.
U.S. Pat. No. 4,348,971, also to Montgomery, discloses a frame consisting of a central torsion beam which extends substantially parallel to the length of the hulls, with cross members secured at right angles to the longitudinal torsion beam, to form a frame. The free ends of the cross members are secured to the hulls. However, this design suffers from the same drawbacks as the earlier Montgomery design enclosed in the U.S. Pat. No. 4,284,024.
U.S. Pat. No. 4,136,414 (Popkin) discloses a design broadly similar to that disclosed in U.S. Pat. No. 4,348,971 in that the frame consists of a central rigid member lying substantially parallel to the spaced hulls, and connected to the hulls by a series of rigid bridging members. In this design, each of the hulls is reinforced by an internal rigid tube which extends substantially the full length of the hull. As with the proposals discussed above, the frame disclosed in U.S. Pat. No. 4,136,414 has to be dismantled for storage or transport, and has the further drawback that the central rigid member is nearly equal to the hulls in length, and cannot be dismantled for storage.
U.S. Pat. No. 4,915,047 (Lord and Collins) discloses a simple generally rectangular frame the sides of which rest on top of the spaced hulls and are secured thereto. The frame includes a large number of components which are push-fitted and pinned together, making assembly/disassembly of the frames relatively complex.
It will be appreciated that, since inflatable catamarans generally are used as recreational boats, and since the whole point of having inflatable hulls is that the hulls can be deflated to a relatively small volume for storage or transport, then it is a considerable advantage if the frame also can be dismantled quickly and easily to a relatively small volume for storage or transport.
U.S. Pat. No. 4,294,184 (Heinrich) which relates to a multi-hull craft rather than to a catamaran as such, discloses a basically triangular frame configuration, in which the spars which extend from the centre hull to the two outer hulls may be pivoted to a position above the centre hull for storage or transport.
However, this frame is attached to the hulls only at a single point on each hull:--thus, the frame does little to stabilise the hulls, and the attachment points tend to be over-stressed, since all the stresses between the frame and the hulls are concentrated at those points.
U.S. Pat. No. 4,930,433 (Tirez) discloses an arrangement in which a frame for joining two surfboards to form a catamaran type of craft has side members which can be pivoted in a horizontal plane for storage or transport of the frame. The pivoting arrangement is such that the frame cannot be collapsed for storage or transport without first detaching the surfboards from the frame. Also, the frame has a geometry which is far from ideal:--the frame members which extend outwards to the outer hulls are secured to those hulls only in a single plane. Thus, the frame is torsionally weak.